Fragrance releasing olefinic silanes

ABSTRACT

Fragrant silanes having the formula: 
     
         (R.sup.1 O).sub.a (R.sup.2 O).sub.b (R.sup.3 O).sub.c (R.sup.4).sub.d 
    
      (R 5 ) e  SiR 6   
     where R 1 , R 2  and R 3  are derived from the group of alcohols consisting of R 1  OH, R 2  OH and R 3  OH wherein R 1  OH, R 2  OH and R 3  OH are fragrant alcohols or alternatively R 1 , R 2  and R 3  are derived from the group of fragrant esters, ketones, or aldehydes having the structure: 
     
         R.sup.7 --CH.sub.2 (C═O)--R.sup.8 
    
     wherein the fragrant ester, ketone or aldehyde is capable of exhibiting the enol form of the carbonyl moiety under reaction conditions, with R 4  and R 5  selected from the group consisting of monovalent hydrocarbon radical having from one to forty carbon atoms and monovalent alkoxy radicals having from one to forty carbon atoms, R 6  a two to forty atom monovalent unsaturated hydrocarbon radical containing a terminal olefinic or acetylenic moiety where the subscript a has a value ranging from 1 to 3 and the subscripts b, c, d, and e have values ranging from 0 to 2 subject to the limitation that a+b+c+d+e=3; R 7  is selected from the group consisting of hydrogen and monovalent hydrocarbon radicals having from one to one hundred carbon atoms and R 8  is selected from the group consisting of hydrogen and monovalent hydrocarbon radicals having from one to one hundred carbon atoms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 09/143,136 filed on Aug.28, 1998 now U.S. Pat. No. 6,046,156 Apr. 4, 2000.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH

Not Applicable

FIELD OF THE INVENTION

The present invention relates to silanes that contain a terminalolefinic moiety and one or more substituent groups derived from fragrantcompounds wherein the fragrant compound is regenerated and released by ahydrolysis reaction.

BACKGROUND OF THE INVENTION

The slow sustained release of a fragrant molecule is a highly desirabletrait in many personal care products. A number of means have beenproposed and implemented to achieve this goal. Among these means aredissolving or suspending fragrant compounds in personal care emulsions(U.S. Pat. Nos. 5,525,588; 5,525,555; 5,490,982; and 5,372,806),encapsulation of a fragrant compound (U.S. Pat. Nos. 5,500,223;5,324,444; 5,185,155; 5,176,903; and 5,130,171), dissolving a fragrantcompound into a hydrophobic phase such as a silicone (U.S. Pat. Nos.5,449,512; 5,160,494 and 5,234,689), incorporation of a fragrantcompound into cross-linked polymers (U.S. Pat. Nos. 5,387,622 and5,387,411), incorporation of fragrant compounds into permeable laminates(U.S. Pat. Nos. 5,071,704 and 5,008,115), incorporation of fragrantcompounds into matrices that soften at body temperature (U.S. Pat. No.4,908,208), incorporation of fragrant compounds into rate controllingmembranes (U.S. Pat. No. 4,445,641) and derivatization of silanes withfragrant alcohols to form alkoxy silanes (U.S. Pat. Nos. 4,524,018 and4,500,725). None of these approaches teach or suggest that anolefinically substituted silane containing one or more fragrantsubstituent groups can be prepared or if prepared would be useful in thepreparation of personal care compositions.

SUMMARY OF THE INVENTION

The present invention provides for the reaction product of a fragrantalcohol and an olefinic halosilane or an olefinic silicon alkoxide. Thepresent invention also provides for a silicon compound having theformula:

    (R.sup.1 O).sub.a (R.sup.2 O).sub.b (R.sup.3 O).sub.c (R.sup.4).sub.d (R.sup.5).sub.e SiR.sup.6

where R¹, R² and R³ are derived from the group of fragrant alcoholsconsisting of R¹ OH, R² OH and R³ OH with R⁴ and R⁵ selected from thegroup consisting of monovalent hydrocarbon radical having from one toforty carbon atoms and monovalent alkoxy radicals having from one toforty carbon atoms, R⁶ a two to forty atom monovalent unsaturatedhydrocarbon radical containing a terminal olefinic or acetylenic moietywhere the subscript a has a value ranging from 1 to 3 and the subscriptsb, c, d, and e have values ranging from 0 to 2 subject to the limitationthat a+b+c+d+e=3.

The present invention further provides for the reaction product of afragrant aldehyde, ketone or ester and an olefinic halosilane or anolefinic silicon alkoxide; and also a silicon compound having theformula:

    (R.sup.1).sub.a (R.sup.2).sub.b (R.sup.3).sub.c (R.sup.4).sub.d (R.sup.5).sub.e SiR.sup.6

where R¹, R² and R³ each independently have the structure:

    R.sup.7 --CH═C(O--)--R.sup.8

wherein R⁷ and R⁸ are independently chosen for each R¹, R² and R³, withR⁴ and R⁵ selected from the group consisting of monovalent hydrocarbonradicals having from one to forty carbon atoms and monovalent alkoxyradicals having from one to forty carbon atoms, R⁶ a two to forty atommonovalent unsaturated hydrocarbon radical containing a terminalolefinic or acetylenic moiety where the subscript a has a value rangingfrom 1 to 3 and the subscripts b, c, d, and e have values ranging from 0to 2 subject to the limitation that a+b+c+d+e=3; R⁷ is selected from thegroup consisting of hydrogen and monovalent hydrocarbon radicals havingfrom one to one hundred carbon atoms and R⁸ is selected from the groupconsisting of hydrogen and monovalent hydrocarbon radicals having fromone to one hundred carbon atoms.

DETAILED DESCRIPTION OF THE INVENTION

The compounds of the present invention introduce fragrant moieties intoan olefinic silane molecule. The olefinic silane molecule is capable offurther reaction under hydrosilylation conditions to form a variety ofsiloxanes that also possess fragrant moieties. These siloxane moleculesare useful in a variety of personal care compositions. The presentinvention is directed to new compositions of matter that are silanesthat release a fragrant alcohol, ester, ketone or aldehyde uponparticular subsequent chemical reactions. Typically the subsequentchemical reaction that releases the fragrant alcohol is a hydrolysisreaction. Furthermore these silanes may be reacted to form siloxanesthat release a fragrant alcohol upon the same particular subsequentchemical reactions wherein the olefinic silane precursor also releases afragrant alcohol, ester, ketone or aldehyde.

The compounds of the present invention are described by the formula:

    (R.sup.1 O).sub.a (R.sup.2 O).sub.b (R.sup.3 O).sub.c (R.sup.4).sub.d (R.sup.5).sub.e SiR.sup.6

where R¹, R² and R³ are selected (or derived from) from the group ofalcohols consisting of R¹ OH, R² OH and R³ OH wherein R¹ OH, R² OH andR³ OH are fragrant alcohols or alternatively are derived from the groupof fragrant esters, ketones, or aldehydes having the structure:

    R.sup.7 --CH.sub.2 (C═O)--R.sup.8

wherein the fragrant ester, ketone or aldehyde is capable of exhibitingthe enol form of the carbonyl moiety under reaction conditions as shown:

    R.sup.7 --CH.sub.2 (C═O)--R.sup.8 →R.sup.7 --CH═C(OH)--R.sup.8

and which will react through the enol hydroxyl group to form acarbon-oxygen-silicon linkage, for example R⁷ --CH═C(O--)--R⁸ where thehyphen after the oxygen in the formula indicates the species is amonovalent radical, with R⁴ and R⁵ selected from the group consisting ofmonovalent hydrocarbon radical having from one to forty carbon atoms andmonovalent alkoxy radicals having from one to forty carbon atoms, R⁶ atwo to forty atom monovalent unsaturated hydrocarbon radical containinga terminal olefinic or acetylenic moiety where the subscript a has avalue ranging from 1 to 3 and the subscripts b, c, d, and e have valuesranging from 0 to 2 subject to the limitation that a+b+c+d+e=3; R⁷ isselected from the group consisting of hydrogen and monovalenthydrocarbon radicals having from one to one hundred carbon atoms and R⁸is selected from the group consisting of hydrogen and monovalenthydrocarbon radicals having from one to one hundred carbon atoms. Itshould be noted that the structure:

    R.sup.7 --CH═C(O--)--R.sup.8

is a conjugate structure that corresponds to the enolate structure:

    R.sup.7 --CH═C(OH)--R.sup.8

but missing the hydroxyl hydrogen. In the structure:

    R.sup.7 --CH═C(O--)--R.sup.8

the hyphen after the oxygen atom indicates a univalent bonding sitewherein the structure is a monovalent radical and through which theradical is bonded as a substituent. Thus when the fragrant moiety isderived from an aldehyde, ketone or ester the fragrant silicon compoundhas the formula:

    (R.sup.1).sub.a (R.sup.2).sub.b (R.sup.3).sub.c (R.sup.4).sub.d (R.sup.5).sub.e SiR.sup.6

where R¹, R² and R³ each independently have the structure:

    R.sup.7 --CH═C(O--)--R.sup.8

with all the variables as previously defined. As used herein the phrasefrom one to one hundred carbon atoms is chosen wherein the class ofavailable fragrant esters, ketones, and aldehydes is subtended by theformula R⁷ --CH₂ (C═O)--R⁸. As used herein, the phrase monovalenthydrocarbon radical includes both aliphatic and aromatic monovalenthydrocarbon radicals that may also include hetero-atoms such as oxygen,nitrogen, sulfur and the halogens, fluorine, chlorine, bromine andiodine.

The following synthetic examples are intended to illustrate the generalsynthetic reactions schemes that a person having ordinary skill in theart of silicones chemistry would typically employ in order to preparethe compounds of the present invention. These reaction schemes are thusillustrative only and do not represent the only synthetic pathways bywhich the compounds of the present invention may be prepared.

When the starting material is a fragrant alcohol such as phenethanol,olefinic halosilanes or olefinic silicon alkoxides may be employed asstarting materials to produce the fragrance-releasing silanes of thepresent invention. Applicant herewith defines the phrase olefinicsilicon alkoxide to be a monomeric silicon compound wherein a singlesilicon atom is substituted with four monovalent organic substituentsone of which is an olefin and one of which is an alkoxide. ##STR1##Where the R groups for reaction III may be Et (C₂ H₅ -) or --CH₂ CH₂ C₆H₅. Similarly3-methyl-5-(2,2,3,-trimethyl-3-cyclopenten-1-yl)-4-penten-2-ol willreact with chloromethylvinylsilane in a similar fashion, reaction schemeIV: ##STR2## as will allyldimethylchlorosilane react with citronellol ina similar, reaction scheme V: ##STR3## An example of the reaction schemeusing a fragrant carbonyl containing moiety,2-methyl-3-(4-t-butylphenyl)propanal, reaction VI: ##STR4## Note thatDMF is dimethylformamide. Reaction scheme VI may also be used to preparethe 3-methyl-3-(3-(1-methylethylphenyl))propanal derivative: ##STR5##The reaction of fragrant carbonyl containing species, i.e. esters,ketones and aldehydes, requires the establishment of the keto enoltautomeric equilibrium previously referred to which is assisted by abase such as triethylamine.

Tautomerism is the chemical phenomenon of the establishment of anequilibrium between two or more structurally distinct compounds. Innearly all cases, the difference between one tautomeric form of theequilibrium compounds and the other is the isomeric placement of ahydrogen atom. A prevalent form of tautomerism is the tautomericequilibrium established between a carbonyl compound (for example onecontaining a carbonyl group) and having a hydrogen atom alpha to thecarbonyl group, for example an α hydrogen: ##STR6## Generally theequilibrium constant favors the keto form and the equilibrium lies wellto the left. The extent of enolization is greatly affected by solvent,concentration and temperature. When a strong base is present, both theenol and the keto form can lose a hydrogen ion (a proton), forming anenolate anion: ##STR7## Since both of these structures differ only inthe placement of electrons, these are canonical forms of the same ionrather than tautomeric isomers. Because oxygen is more electronegativethan carbon, the predominate canonical form is the one where the ioniccharge is more localized on the oxygen atom. While the tautomericequilibrium between enols and ketones or aldehydes is not normally apreparative reaction, the equilibrium must occur since ketones andaldehydes often react through their enol forms as they do instantly inthe preparation of the compounds of the present invention. For a moredetailed explanation of this chemistry see J. March "Advanced OrganicChemistry," John Wiley & Sons, New York (1985), pp. 66-68 and 527-529and references therein.

The fragrant alcohols that are precursors of the silanes of the presentinvention are selected from the group consisting of3-methyl-5-(2,2,3,-trimethyl-3-cyclopenten-1-yl)4-penten-2-ol,2-methylbutanol, 3-pentanol, n-pentanol, 2-pentanol, n-hexanol,2-methylpentanol, 1-decanol, sandela, nonadyl, dimetol, thymol,1-heptanol, menthol, eugenol, vanillan, o-vanillan,4-(p-hydroxyphenyl)-2-butanone, syringealdehyde, prenol, cis-3-hexanol,trans-3-hexanol, cis-4-heptenol, trans-2-octenol,trans-2-cis-6-nonadienol, geraniol, nerol, citronellol, crotyl alcohol,oleyl alcohol, linalool, α-terpineol, β-phenethyl alcohol, cinnamicalcohol, benzyl alcohol, α-methylbenzyl alcohol, nonyl alcohol,1-octanol, 3-octanol, phenethyl salicylate, hydrocinnayl alcohol,cis-6-nonen-1-ol, trans-2-nonen-1-ol, methyl salicylate, cis-3-octen-ol,anisyl alcohol, carvacrol, dihydrocarveol, benzyl salicylate,tetrahydrogeraniol, ethyl salicylate, ethyl vanillin, isoeugenol,isopulegol, lauryl alcohol, tetrahydrolinalool and 2-phenoxyethanol.

The fragrant carbonyl containing species are selected from the groupconsisting of 3-methyl-3-(3-(1-methylethylphenyl))propanal,2-methyl-3-(4-t-butylphenyl)propanal, 3-phenylpropional,2-phenylpropional, propional, isobutyral, 2-methylbutyral, hexanal,octanal, nonanal, decanal, 3,7-dimethyl-1-al, p-tolylacetaldehyde,phenylacetaldehyde,4-(3)(4-methyl-3-pentenyl)-3-cyclohexen-carbaldehyde,2,6-dimethyl-5-heptenal, 3,7-dimethyl-2,6-octadienal, trans-4-decenal,cyclamen aldehyde, 4-(p-methoxyphenyl)-2-butanone, acetophenone,2-pentanone, 2-butanone, 2-heptanone, 3-heptanone, 2-decanone,3-penten-2-one, 6-methyl-5-hepten-2-one, geranylacetone, ionone,5-methyl-alpha-ionone, 2-acetonaphtone, 2-methyl-3-phenylpropan-2-ylacetate, linalyl acetate, menthanyl acetate, 2-phenylethyl acetate,tetrahydrolinalyl acetate, phenethyl propionate, phenethylhexanoate, andbutyl acetate.

The fragrance releasing compounds of the present invention areparticularly suited to incorporation into personal care products toimpart a desirable long lasting fragrance to the products. Suitable usesinclude but are not limited to deodorants, antiperspirants, skin creams,facial creams, hair care products such as shampoos, mousses, stylinggels, protective creams, shaving creams, after shave, cologne, perfume,color cosmetics such as lipsticks, foundations, blushes, makeup, andmascara; and other cosmetic formulations where other silicon containingcomponents have been added and where it is desirable to impart afragrance. Incorporation of small amounts of the compositions of thepresent invention into fragrance products such as shaving lotions,colognes, toilet water, and perfumes can impart a desirable long lastingfragrance to these products. Further, the silanes of the presentinvention may incorporated into other products where it is desirable tomask unpleasant odors with a pleasant fragrance for example householdcleaning products such as waxes and polishes, automobile cleaningproducts such as waxes and polishes, detergents, textile coatings,paints, varnishes and the like subject to the limitation that the silaneof the present invention be compatible or capable of being renderedcompatible with the product in which it is incorporated.

Experimental

Preparation ofDimethylvinylphenethyloxysilane,--Dimethylvinylchlorosilane (150 mL,1.099 moles) was added to a stirred solution of phenethyl alcohol (124.5mL, 1.042 moles), triethylamine (TEA, 155 mL, 1.112 moles) and toluene(300 mL) over 1.5 h. After addition, the reaction was heated to 65° C.for 0.5 h then cooled to room temperature, filtered, the filter cakewashed with toluene (200 mL), the filtrate concentrated in vacuo andthen vacuum distilled (81-85° C./4 mm Hg) to give product (180.5 g,84%).

Bis(phenethyloxy)methylvinylsilane,--Dichloromethylvinylsilane (80 g,0.567 moles) was added to a stirred solution of phenethyl alcohol (140g, 114 moles), triethylamine (TEA, 121 g, 1.2 moles) and Isopar C (700mL) over one hour during which time the reaction mixture was heated to70° C. After an additional one hour, the reaction was cooled to roomtemperature, filtered, concentrated in vacuo and then stripped underhigh vacuum distilled (110° C. at 4 mm Hg) to give product (166 g, 94%).

Phenethyloxydiethoxymethylvinylsilane,--Triethoxyvinylsilane (200 g,1.05 moles), phenethyl alcohol (128 g, 1.05 moles) and Filtrol-20(5 g)were added together and heated to 90° C. Ethanol (EtOH) was distilledoff as it formed and the reaction was stopped when most of the phenethylalcohol had been consumed. The reaction mixture was then stripped at 90°C./4 mm Hg to give a mixture of products which had the followingdistribution: 45% product in which both OR=OEt, 39% product in which oneOR=OEt and one OR=phenethyloxy, and 8% product in which both OR=phenethyloxy.

Dimethyl(3-methyl-5-(2,2,3,-trimethyl-3-cyclopenten-1-yl)-4-penten-2-oxy)vinylsilane,--Dimethylchlorovinylsilane(10.0 mL, 0.073 moles) diluted with toluene (25 mL), was added to astirred solution of3-methyl-5-(2,2,3,-trimethyl-3-cyclopenten-1-yl)4-penten-2-ol (16.40 g,0.077 moles), triethylamine (TEA, 7.8 g, 0.077 moles) and toluene (100mL) over 20 min during. The mixture was then heated to 60° C. After 6hours, the reaction was cooled to room temperature, filtered,concentrated in vacuo and then stripped and distilled under high vacuumdistilled (75-77° C./0.3 mm Hg) to give product (166 g, 94%).

Dimethylvinyl(2-methyl-3-(4-t-butylphenyl)propenoxy)silane--A 100 mL3-neck round bottom flask equipped with a stir-bar, a thermometer, acondenser and a nitrogen inlet was charged withdimethylvinylchlorosilane (4.1 mL, 0.030 moles),2-methyl-3-(4-t-butylphenyl)propanal, (5.0 g, 0.024 moles),triethylamine and N,N-dimethylformamide (DMF, 20 mL) and heated to 80°C. for 22 h. the mixture was diluted with 100 mL of Isopar-C, and themixture was washed three times with cold saturated aqueous sodiumbicarbonate, then cold 1N HCl, then bicarbonate, then dried over MgSO₄and stripped to give 6.4 g (90%) product.

Dimethyl(3-methyl-3-(1-methylethylphenyl)propenoxy)vinylsilane--A 500 mL3-neck round bottom flask equipped with a stir-bar, a thermometer, acondenser and a nitrogen inlet was charged withdimethylvinylchlorosilane (44 mL, 0.322 moles),3-methyl-3-(3-(1-methylethylphenyl))propanal (50 g, 0.263 moles),triethylamine (90 mL, 0.644 moles) and N,N-dimethylformamide (DMF, 200mL) and heated to 80° C. for 22 h. The mixture was diluted with 200 mLof Isopar-C, and the mixture was washed three times with cold saturatedaqueous sodium bicarbonate, then cold 1N HCl, then bicarbonate, thendried over MgSO₄ and stripped and distilled (85-95° C./0.07 mm Hg) togive 40.7 g (61%) product.

Dimethyl(4-methyl-2-penten-2-oxy)vinylsilane--A 500 mL 3-neck roundbottom flask equipped with a stir-bar, a thermometer, a condenser and anitrogen inlet was charged with dimethylvinylchlorosilane (14.5 g, 0.12moles), 4-methyl-2-pentanone (10 g, 0.10 moles), triethylamine (24.3 g,0.24 moles) and N,N-dimethylformamide (DMF, 75 mL) and heated to 80° C.for 40 h. The mixture was filtered to remove solid, diluted with 100 mLwater, then extracted with hexanes (3×100 mL). The extracts werecombined, washed with water (2×50 mL), then dried over MgSO₄ andstripped and distilled (160-162° C.) to give 10.1 g (55%) product.

What is claimed is:
 1. A silicon compound having the formula:

    (R.sup.1).sub.a (R.sup.2).sub.b (R.sup.3).sub.c (R.sup.4).sub.d (R.sup.5).sub.e SiR.sup.6

where R¹, R² and R³ and are derived from the group of fragrant aldehyde,ketone or ester consisting of3-methyl-3(3-(1-methylethylphenyl))propanal),2-methyl-3-(4-t-butylphenyl)propanal, 3-phenylpropional,2-phenylpropional, propional, isobutyral, 2-methylbutyral, hexanal,octanal, nonanal, decanal, 3,7-dimethyl-1-al, p-tolylacetaldehyde,phenylacetaldehyde,4-(3)(4-methyl-3-pentenyl)-3-cyclohexen-carbaldehyde,2,6-dimethyl-5-heptenal, 3,7-dimethyl-2,6-octadienal, trans-4-decenal,cyclamenaldehyde, 4-(p-methoxyphenyl)-2butanone, acetophenone,2-pentanone, 2-butanone, 2-heptanone, 3-heptanone, 2-decanone,3-penten-2-one, 6-methyl-5-hepten-2-one, geranylacetone, ionone,5-methyl-alpha-ionone, 2-acetonaphtone, 2-methyl-3-phenylpropan-2-ylacetate, linalyl acetate, menthanyl acetate, 2-phenylethyl acetate,tetrahydrolinalyl acetate, phenethyl propionate, phenethylhexanoate, andbutyl acetate; and R⁵ selected from the group consisting of monovalenthydrocarbon radicals having from one to forty carbon atoms andmonovalent alkoxy radicals having from one to forty carbon atoms, R⁶ atwo to forty atom monovalent unsaturated hydrocarbon radical containinga terminal olefinic or acetylenic moiety, where the subscript a has avalue ranging from 1 to 3 and the subscripts b, c, d, and e have valuesranging from 0 to 2 subject to the limitation that a+b+c+d+e=3.
 2. Thesilicon compound of claim 1, wherein the subscript a has a value of 2.3. The silicon compound of claim 1, wherein the subscript a has a valueof
 3. 4. A composition comprising a silicon compound having the formula:

    (R.sup.1).sub.a (R.sup.2).sub.b (R.sup.3).sub.c (R.sup.4).sub.d (R.sup.5).sub.e SiR.sup.6

where R¹, R² and R³ and are derived from the group of fragrant aldehyde,ketone or ester consisting of3-methyl-3(3-(1-methylethylphenyl))propanal),2-methyl-3-(4-t-butylphenyl)propanal, 3-phenylpropional,2-phenylpropional, propional, isobutyral, 2-methylbutyral, hexanal,octanal, nonanal, decanal, 3,7-dimethyl-1-al, p-tolylacetaldehyde,phenylacetaldehyde,4-(3)(4-methyl-3-pentenyl)-3-cyclohexen-carbaldehyde,2,6-dimethyl-5-heptenal, 3 ,7-dimethyl-2,6-octadienal, trans-4-decenal,cyclamenaldehyde, 4-(p-methoxyphenyl)-2butanone, acetophenone,2-pentanone, 2-butanone, 2-heptanone, 3-heptanone, 2-decanone,3-penten-2-one, 6-methyl-5-hepten-2-one, geranylacetone, ionone,5-methyl-alpha-ionone, 2-acetonaphtone, 2-methyl-3-phenylpropan-2-ylacetate, linalyl acetate, menthanyl acetate, 2-phenylethyl acetate,tetrahydrolinalyl acetate, phenethyl propionate, phenethylhexanoate, andbutyl acetate; with R⁴ and R⁵ selected from the group consisting ofmonovalent hydrocarbon radicals having from one to forty carbon atomsand monovalent alkoxy radicals having from one to forty carbon atoms, R⁶a two to forty atom monovalent unsaturated hydrocarbon radicalcontaining a terminal olefinic or acetylenic moiety, where the subscripta has a value ranging from 1 to 3 and the subscripts b, c, d, and e havevalues ranging from 0 to 2 subject to the limitation that a+b+c+d+e=3.5. The composition of claim 4 wherein the subscript a has a value of 2.6. The composition of claim 4 wherein the subscript a has a value of 3.7. A cosmetic composition comprising the composition of claim 4.